Continuous casting mold having insulated portions



5 Sheets-Sheet 1 4 5 9 9 /W 7 1 i/ a i 2 Eli 5 F i? H v v C VZ F n u 2 3 2 i Q nw l 2 M. HESS July 14, 1970 CONTINUOUS CASTING -MOLD HAVING INSULATED PORTIONS Filed Oct. 19, 1967 FIG. 3

July 14,1970

CONTINUOUS CASTING MOLD HAVING INSULATED PORTIONS Filed Oct. 19, 1967 M. HESS 3 Sheets-Sheet 2 MARTIN HESS July 14, 1970 M. HESS 3,520,352

CONTINUOUS CASTINGMOLD HAVING INSULATED PORTIONS Filed Oct. 19, 1967 3 Sheets-Sheet 3 INVENTOR. MAP TIN HE$$ BY HQMM Ms dfllomg United States Patent O 3,520,352 CONTINUOUS CASTING MOLD HAVING INSULATED PORTIONS Martin Hess, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Continuation-impart of application Ser. No. 503,251,

Oct. 23, 1965. This application Oct. 19, 1967, Ser.

Int. Cl. B22d 11/00 US. Cl. 164-283 Claims ABSTRACT OF THE DISCLOSURE A continuous casting mold that enhances heat transfer and reduces the formation of corner cracks comprises a shell that is water cooled, but which is so made that the formation in the mold of a rigid continuous envelope is avoided until just before the strand emerges from the mold when the skin or shell becomes continuous and rigid enough to contain the molten metal of the core.

CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 503,251 filed Oct. 23, 1965 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to continuous casting and more particularly to a casting mold for use in producing a continuous strand of metal.

In the continuous casting metals, and particularly steel, it is desirable to transfer heat as rapidly as possible away from the casting within the casting mold, for then the casting becomes completely solidified in a shorter metallurgical length or depth of pool. Consequently, the casting can be bent toward the horizontal sooner, and the overall height of the continuous casting machine can be significantly reduced. As it is understood in the art, metallurgical length or depth of pool is the distance measured along the axis of the cast strand the molten metal extends from the meniscus of the molten metal to the point where the strand is completely solidified.

Studies of the continuous casting of metals in a mold reveal that two relatively different zones of metal state are present in the mold. A relatively shallow first zone of molten metal, surrounded by a thin skin of solid metal, exists near the top of the mold; the depth of this first zone being in the order of a few inches or less. Below this first zone is a second zone wherein the casting strand has developed an outer skin which is thicker and relatively rigid.

The rate of heat transfer from the molten metal to the walls of the mold, which are generally water cooled, is greater in the first zone than in the second zone. It has been found, for example, that about sixty percent of the heat that is removed from the molten metal within molds as heretofore known in the prior art, is removed in a first zone, and only about ten percent of the heat removed in such molds is removed in a second zone. The reason for this difference is that, immediately as the skin becomes rigid in the second zone, there is a contraction of metal and the solid skin shrinks away from intimate contact with the mold walls. Thus, an air gap is formed between the skin of the cast strand and the mold wall, and the rate of heat transfer from the molten metal in this second zone is significantly reduced.

The present invention prevents the complete formation of a skin around the perimeter of the casting until a great percentage of heat has been removed from the molten metal within the mold. Consequently, the metallurgical length of the casting, formed in the mold of the invention, is significantly shorter than in castings made under present practice.

SUMMARY OF THE INVENTION According to the invention, molten metal in a continuous casting mold is differentially surface cooled in a first zone extending along the length of the mold, and a rigid skin of solid metal does not completely contain the molten metal of the core. When the casting moves into an adjacent zone wherein there is no differential cooling the skin completely contains the molten core. Thereafter, the cast strand emerges from the mold with a skin that is thicker and a metallurgical length that is less than in strands made in accordance with molds of the prior art teaching.

Further, in accordance with this invention, solid portion of the skin remains in contact with the mold walls for a longer period of time than under conventional practice, and a greater percentage of the total heat in the molten metal is removed while the casting is within the mold.

It has been found that this invention greatly reduces the tendency for corner cracks to form, that have heretofore plagued the art.

For a further understanding of the present invention and for advantages and features thereof, reference may be made to the following description taken in conjunction with the accompanying drawings which show for the purpose of exemplification embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic representation of a portion of a continuous casting machine, including the casting mold of the present invention;

FIG. 2 is a transverse sectional view along line IIII of FIG. 1;

FIG. 3 is a transverse sectional view along line III-III of FIG. 1;

FIG. 4 is a transverse sectional view along line IVIV of FIG. 1;

FIG. 5 is a transverse sectional view, similar to FIG. 2; of a first other embodiment of the mold of FIG. 1;

FIG. 6 is a sectional view along line VIVI of FIG.

FIG. 7 is a transverse sectional view, similar to FIG. 2, of a second other embodiment of the mold in FIG. 1;

FIG. 8 is a transverse sectional view, similar to FIG. 2, of a third other embodiment of the mold of FIG. 1;

FIG. 9 is a view taken along line IXIX of FIG. 8;

FIG. 10 is a transverse sectional view, similar to FIG. 4, of the embodiment of the mold illustrated in FIG. 8;

FIG. 11 is a transverse sectional view, similar to FIG. 4, of a fourth other embodiment of the mold; and

FIG. 12 is a transverse sectional view, similar to FIG. 4, of a fifth other embodiment of the mold.

DETAILED DESCRIPTION A continuous casting mold, in accordance with the present invention,.is designated generally as 11 in FIGS. 1 and 2, and includes: a molten metal casting cavity 13, which is generally square in the embodiment illustrated, but which may be round, elliptical, polygonal or any other suitable shape, and which is bounded by vertical, mutually intersecting first wall portions 15, and second or corner wall portions, 17, situated in the top portion of the mold (see FIG. 1). A fluid retentive envelope 19 surrounds the walls 15 and corner members 17 of the casting cavity in spaced apart relation thereto. Envelope 19 is adapted to receive a cooling fluid, such as water, via

an inlet conduit 21, and to discharge the cooling fluid via an outlet conduit 23.

While the first wall portions 15 are preferably made of a highly thermal conductive material such as copper, the second or corner wall portions 17 are constructed of a lesser thermally conductive material, such as, for example, a ceramic material. As shown in FIG. I, the corner wall portions 17 have a generally L-shaped or angular cross section, and the vertical edges of each corner portion slope downwardly and convergently toward each other. Thus, the corner member 17 terminates at some convenient level in the mold above of the discharge end of the mold which, as shown in FIG. 1, is between the transverse sections at lines IIIIII and IV--IV.

Referring to FIG. 2, it will be noticed that each vertical edge of each corner portion 17 is rabbeted to receive the walls 15, which may be secured to the corner portions by cap screws (not shown), or any other suitable manner, so that the inner surfaces of the walls 15 and corner portions 17 are substantially coplanar. It should be understood, that the corner portions 17 may terminate at any convenient level in the mold 11, and the termination point suggested in FIG. 1 is not necessarily determinative in all installations.

From FIG. 2, it will be noticed that each side or leg of the ceramic corner portions 17 at the top extends about one-fourth the length of each side, and that the metallic wall portion 15, at the same level in the mold, is about one-half the length of the side of the mold. At the level of FIG. 3, however, the sides or legs of the ceramic corner portions 17 now extend only about one-tenth of the length of each side of the mold, and the metallic wall portion 15 extends about eight-tenths of the side of the mold. In FIG. 4, which is a sectional view taken below the bottom of the corner portions 17, there are, of course, no corner portions 17, and the metallic wall portion 15 extends the full length of each side of the square shaped mold 11.

FIG. illustrates a cross sectional view of a casting mold which is similar to the mold of FIG. 2, but wherein the ceramic corner portions 29 include an arcuate outer body portion and an inner angularly shaped body portion 31, which projects inwardly of the casting cavity and generally diagonally across the square shaped m'old 11. The angularly shaped body portion 31 may have any shape and for exemplification herein has a triangular cross sectional shape. The arcuate body portion 29 is provided, as are the ceramic corner portions in FIG. 2, with vertical grooves 24 or rabbets in which the walls fit and to which the walls may be secured by suitable fastening means, as discussed hereinbefore.

The embodiment of the mold 11 illustrated in FIG. 7 discloses a second wall portion 33 which includes an angle shaped member 34 that is maintained in spaced apart relation to an extending portion of the walls 15 by vertical spacer bars 35. The space 37 between the angle shaped member 34 and the extended portion of the walls 15 may be filed with a suitable insulating material or, the space may constitute an air space. The top and bottom of the space 37, of course, would be sealed to prevent cooling fluid from entering thereinto; such cooling fluid being normally present in the space between the mold walls 15 and the envelope 19.

Those skilled in the art will appreciate that in each of the embodiments of the invention discussed hereinabove, the corner members or wall portions 17 effect a retardation of the cooling of the molten metal in intimate contact with the wall portions 17 that are disposed in the areas of the corners of the mold. In some applications, however, it may be desirable to retard the cooling of the molten metal at the middle region of the walls 15, as shown in FIG. 8. In these instances, there is provided a trapezoidal shaped insulating member 39, which may be fixed to the walls 15 in any suitable manner; preferably, the insulating member is made of a refractory or ceramiclike material. The insulating member 39 in such cases is provided with an air space 41 between the wall 15 and the main body portion of the insulating member 39. In some instances, the trapezoidal shaped insulating member 39 may be made of metal, and the space 41, between the member 39 and the wall 15, may be filled with a suitable insulating material, or at least the space 41 may constitute an air space, as does the space 37 in FIG. 7.

In operating the conventional continuous casting machine, molten metal flows from a tundish into a casting mold that reciprocates vertically and a cast strand of metal is continuously withdrawn from the mold by conventional means such as pinch rolls. The molten metal is first chilled in the mold upon contacting the cooler mold walls in what may be considered as a first cooling zone. Initially, heat is rapidly removed from the molten metal in this zone and, according to current theory, a skin is formed completely around a central pool of molten metal. The initial formation of the skin is the beginning of the casting.

Thereafter, as the skin thickens and as the casting is withdrawn from the mold, at some level below the meniscus of the molten metal, the casting shrinks away from the rapid heat transfer, which occurs in the first zone, is significantly reduced. In fact, the depth of the molten metal in the first zone is relatively shallow, and during most of the time the casting is in the mold the skin is not in intimate contact with the mold walls.

As soon as the casting leaves the mold, water is sprayed on the outer surface of the casting to cool the surface and to build up a skin thickness that will retain the molten metal comprising the central liquid core of the casting. The central region of the casting remains liquid for a considerable distance below the meniscus, and the distance from the meniscus to the point at which complete solidification of the casting occurs is termed the metallurgical length of depth of pool. Experience teaches, that it is necessary to delay bending of the vertical casting toward the horizontal until the casting has completely solidified in order to avoid damaging the cast strand. This means that in the usual continuous casting machine the mold is elevated considerably above the working ground level, principally because of the excessive metallurgical length in steel castings.

In contrast to the conventional apparatus and method practice, molten metal 43 flows from a tundish 45 into a casting cavity 13 of the mold 11 and a cast strand 47 forms in the casting cavity and is withdrawn from the mold by pinch rolls (not shown), or by any other suitable mechanism.

The following describes what is believed to happen in the mold 11 of the present invention after withdrawing of the casting has become continuous, and as the molten metal 43 is poured into the mold 11. The molten metal 43 entering the first zone of the casting cavity is chilled by contact with the Water-cooled, metallic portion mold walls 15 which comprise the middle portion of each side of the cast strand 47 in this zone. The molten metal 43 which contacts the cooler mold walls 15 loses heat rapidly to the fluid 48 in the space between the mold walls and the envelope, and a part 49 of the skin of the casting commenses to form adjacent the water cooled mold surfaces, as shown in FIG. 2. At the corner portions 17 however, there is no intimate contact of molten metal 43 with a cool wall surface, since the corner portions 17 are made of ceramic or the like material, and so, in the corner regions of the first zone, the molten metal 43 remains liquid. FIG. 2 depicts what is believed to be a representative cross section of the condition within the first casting zone, at the level IIII in FIG. 1; this first zone level being just below the meniscus of the liquid molten metal 43. It will be noticed that, adjacent the first wall portions 15 on each side of the mold, the metal has formed a portion of a solid skin in regions designated 49, but that in the region proximate to each corner wall portion 17, the metal 43 is still molten and no skin forms at the corners. It should be remembered, however, that the corner wall portions 17 taper vertically in a converging manner. FIG. 3, therefore, depicts the situation (in a manner similar to FIG. 2) at a slightly lower level in the mold.

In FIG. 3, the metallic wall portions 15 are now longer, or wider as the case may be, and at the level of FIG. 3, a greater portion of liquid metal 43 comes into contact with the water cooled metallic wall portions 15. Yet, not all of the molten metal has come into contact with a cooler wall surface, and the skin does not completely surround the molten metal. At the corner wall portions 17 in FIG. 3, there is still discontinuity of the skin 49. It should be pointed out that, because the solid portions 49 at each of side of the casting have not joined at the corners, there is no tendency for the partially solidified wall portions 49 to cause stresses at the corners and form corner cracks, which are commonly found in castings made according to present practice.

In FIG. 4, which is a view below the bottom of the corner wall portions 17, the molten metal condition at the corners, as shown in FIGS. 2 and 3, had disappeared, because, at the level of FIG. 4, all of the molten metal at the corners contacts the mold walls 15 and is chilled by the cooling fluid or water. Thus, solidification also occurs at the corners, designated 51, and this newly solidified metal is joined to the already solidified portions 49, to form a rigid closed skin which is the start of a continuous cast strand having a cross section which is believed to be substantially as shown in FIG. 4. It should be noticed that, because of the delayed solidification at the corners, there is little or no tendency for the casting to form the conventional air gap between the solidified portion 49 and the chilled mold wall 15, not at least until the cast strand 47 is about to emerge from the mold 11.

It should be recognized by those skilled in the art that the average thickness of the skin of the casting 47, produced in the mold 11 of the present invention, is significantly thicker than the skin of a casting made in a conventional type of continuous casting mold. The skin is significantly thicker because there has been intimate contact of the solid skin portions with the cooler mold walls, and a greater heat transfer, for a longer period of time, since there is no air-gap in the region where there is differential surface cooling of the cast strand.

Such a significant increase in the average skin thickness means that the metallurgical length or depth of pool will be considerably shorter in castings made in the mold 11, than the metallurgical length of conventional castings. This reduction in metallurgical length means that the overall height of a casting machine, using a mold of the type shown in FIG. 1, can be significantly reduced from present proportions.

A casting mold 11, having the cross section shown in FIG. 5, operates in the same manner to reduce and to delay solidification, of molten metal at the corners, in the same manner as described hereinbefore. Likewise, a mold having a cross section similar to FIG. 7 will reduce the tendency of the molten metal to solidify at the corners for the reasons mentioned hereinbefore.

The formation of a cast strand 47, in a casting cavity which contains the molten metal 43 within a mold 11 having the cross sectional shape shown in FIG. 8, occurs in a slightly different manner. In the embodiment of the mold 11 shown in FIG. 8, the insulated second wall portions 39 occur at the midlength of the sides and the first or corner wall portions of the mold are chilled. Therefore, the molten metal 43 solidifies initially at the corners, as at 55.

It should be noticed, however, that even in the embodiment of the invention shown in FIG. 8, the skin of the casting does not become closed and rigid until the casting strand moves downward to about the level of XX in FIG. 9, at which the cross section has a shape about as shown in FIG. 10. Since even in this embodiment of the invention the skin does not form a rigid closed envelope around the molten metal core, the skin cannot shrink away from the mold wall. Thus here too, more effective heat transfer occurs between the molten metal and the coolant surrounding the mold.

In the embodiment of FIGS. 8-10, there is a considerable thickness of the skin at the corners, and a relatively lesser skin thickness along the lateral sides of the casting. But, in this instance also, the average thickness of the skin of the cast strand 47 is significantly greater than the skin of a continuous strand of cast metal made in molds of conventional design.

FIG. 11 illustrates the cross section of a continuous casting mold 57 wherein ceramic corner portions 59 are located only at diagonally opposite corners. Thus, the skin 49 of the cast strand does not become closed and rigid, because of the two discontinuities at the ceramic corner portions, until the cast strand moves downward below the level at the bottom of the ceramic corner portions 59.

In like manner, FIG. 12 illustrates the cross section of a continuous casting molding 61 wherein a single ceramic corner portion 63 is used; such single ceramic corner portion also prevents the skin 49 of the cast strand from becoming a closed and rigid envelope until the cast strand moves downward below the level at the bottom of the ceramic corner portion 63.

Since the diagonally opposite ceramic corner portions 59, as well as the single ceramic corner portion, effectively prevent the formation of a closed rigid skin the usual air gap between the skin and the mold wall does not form and considerably more heat transfers from the molten metal core to the cooling fiuid 48.

Consequently, the metallurgical length is shorter and continuous casting machines utilizing the mold 11 have a significantly lower or overall height.

In accordance with the present invention, a cast strand emerging from the mold 11 has a thicker skin that will not break out as readily as the skin of strands cast in conventional type molds.

The present invention is directed to a continuous casting mold that significantly increases the overall removal of heat from the molten metal and at the same time avoids or minimizes the occurrence of surface cracks, particularly, at the corners of the cast strand. The significant increase in the overall removal of heat is accomplished by not allowing the skin to form a closed rigid envelope around the molten core or pool, as is customary in conventional continuous casting molds. As long as the skin does not form a closed rigid envelope, the partially solidified metal 49 (FIGS. 2, 3) maintains intimate contact with the metallic portion 15 of the mold wall, and greater and more effective heat transfer occurs between the molten metal and the cooling medium 48 surrounding the walls 15 of the mold. The usual air gap between the rigid skin and the mold wall cannot form as long as there is no continuity in the rigid skin, which is a significant feature of the present invention.

An important feature of the present invention is that, at the corners of the mold, there is no continuity in the skin of the casting, and corner cracks, which usually form in the corner regions of ordinary molds, do not occur in molds constructed according to the present invention. The corner wall portions of the present invention prevent premature cooling of the molten metal in the corner regions and in some applications along the side walls, thereby, prevent the formation of corner cracks, as well and avoiding the formation of a closed rigid skin as mentioned hereinabove.

It is important to note that the corner wall portions 17 taper convergently toward the bottom so that here is a gradual enlargemen of the solid skin portion; that is to say, the solid skin portion becomes thicker at the midlength of the cooled wall portions 15 and thinner near the corners. At a level just below the corner wall portions 17,

the molten metal solidifies quite rapidly and the skin becomes rigid enough to contain the molten metal core. At the level just above the bottom of the mold, the skin shrinks away from the mold wall and an air gap 50 forms between the skin and the mold wall but this air gap is relatively short in vertical height.

Another feature of the present invention is found in the increased rate of production of a cast strand in a continuous casting machine utilizing the mold 11. It is generally recognized that there is a critical rate of descent for a cast strand of any given cross section. Exceeding this critical rate may result in a metallurgical length of depth of pool so deep that the skin may be warped and easily broken by tensile and hydrostatic stresses exerted by the metal within the molten core. Thus, it is necessary to withdraw the casting from the mold at a rate which will allow the casting to build sufiicient skin thickness that can resist such tensile and hydrostatic stresses. Thus, because the mold 11 produces a rigid skin having a relatively greater than usual thickness, the metallurgical length is significantly shorter and a continuous casting machine utilizing the mold 11 can produce a continuous strand of cast metal at a faster rate than conventional machines.

A continuous casting machine utilizing the mold 11 of the present invention produces a continuous strand of cast metal that is devoid, or has a minimum number of, corner cracks and tears which frequently are found in castings produced in conventional molds. Corner cracks and tears are frequently the reason why a continuous strand of metal has to be rejected; and so, a continuous casting machine utilizing the mold 111 will produce more acceptable cast strands than conventional machines and thus will be more efiicient in operation.

A frequent cause of rejection of continuous cast strands is deformity in cross section. That is, the billet is not rectangular in cross section, but has a rhornbic shape. The rhornbic shape is due to a more rapid cooling at an opposite pair of corners whereby the metal at these corners shrinks further away from the mold than the metal at the other opposite pair of corners. In the mold 11 of the present invention, however, there is no tendency for one pair of opposite corners to solidify faster than the other pair of corners, since all of the corners remain molten for the same period of time. In the present invention the cooling and solidification of the metal at the corners is retarded equally; hence, the billet produced in a continuous casting machine using the mold 11 will be more nearly rectangular than billets cast in a conventional machine.

While the foregoing has described a continuous casting mold having a rectangular or square shape it will be understood that in the casting of cylindrical shapes, insulating bafiles similar to the triangular shaped baffles 31 may be disposed in angular spaced relation around the circumference of a circular shape so that solidification of the skin of a circular or cylindrical casting may be delayed in spaced apart areas or regions similar to the corner regions mentioned before. Likewise, such baffies as depicted in FIG. 5 may be disposed at the corners of continuous cast strands having any polygonal shape or cross section.

Although the invention has been described herein with a certain degree of particularity, it is understood that the present invention disclosure has been made only as an example and that various modifications and changes may be made within the scope of the invention as defined by the appended claims.

What is claimed is:

1. A continuous casting mold that receives molten metal and from which a partially solidified cast strand continuously emerges, comprising:

(a) a wall having a first portion extending both partially around the perimeter and axially along the length of said mold, and terminating anteriorly of the discharge end thereof,

(b) said first portion tapering so as to have more surface area at the inlet end thereof in contact with the molten metal than at the other end thereof,

(c) said first portion having lower heat conductivity than said wall.

2. The structure of claim 1 wherein:

(a) said mold is polygonal in cross section and (b) said first wall portion includes abutting areas of adjacent sides of said mold.

3. The structure of claim 1 wherein:

(a) said mold is polygonal in cross section and (b) said first wall portion includes a portion of the area of one of the sides of said mold.

4. The structure of claim 1 wherein:

(a) said first wall portion includes abutting areas of adjacent sides of said mold at two or more corners of said mold.

5. The structure of claim 4 wherein:

(a) said mold is rectangular in cross section; and

(b) said corners are diagonally opposite.

6. In a continuous casting machine wherein molten metal flows into the casting cavity of a mold defined by Walls and a partially solidified cast strand continuously emerges from the discharge end thereof, the improvement comprising:

(a) a fluid cooling the exterior of said mold wall,

(i) said wall having a first portion extending both partially around the perimeter and axially along the length of the mold,

(ii) said first wall portion terminating anteriorly of the discharge end of said casting cavity, with (iii) said first wall portion tapering so as to have a greater surface area in contact with molten metal at the inlet end of said first wall portion than at the other end thereof, with (iv) said first portion being comprised of abutting areas of adjacent sides of said mold,

(v) said first wall portion being capable of transferring heat from said molten metal to said fluid at a rate that is less than the rate at which heat is transferred from said molten metal to said fluid by the remaining portion of the mold wall, whereby the molten metal adjacent said first portion remains molten.

7. A continuous casting mold comprising:

(a) a wall defining a casting cavity having one end through which molten metal enters and a discharge end from which a cast strand continuously emerges, said cast strand comprising a solid skin of metal surrounding and containing a core of molten metal that gradually solidifies; and

(b) cooling medium contacting and removing heat from the wall of said mold, said wall including (i) a first zone comprised of first and second inset laterally abutting areas,

(1) said first area tapering so as to have a greater lateral dimension in contact with said molten metal adjacent the inlet end than adjacent the discharge end of said lIl'lOld, and so constructed that the molten metal in contact with said first area is maintained in a molten state,

(2) said second area extending partially around the perimeter of said mold and being so constructed that heat transfers to said cooling medium at a rate such that said molten metal solidifies adjacent said second area to partially form said skin;

(ii) a second zone axially abutting said first zone and disposed anteriorly of the discharge end of said mold, said second zone being so constructed that the molten metal in contact with the surface of said first area contacts said second zone and solidifies to completely form said skin within said mold.

8. The structure of claim 7 wherein: and completing the formation of said solid skin (a) said mold is polygonal in cross section; and within said mold. (b) said first area is a surface of a ceramic material 15. A continuous casting mold that receives molten located at one corner of said polygonal shaped mold. metal at one end, from the other end of which a partially 9. The structure of claim 7 wherein: solidified cast strand emerges along the axis of said mold, (a) said mold is polygonal in cross section; comprising:

(b) said first area is a surface of a ceramic material located at diagonally opposite corners of said polygonal mold; and

(c) said second area is a surface of a metallic material.

(a) a first surface portion of said mold in contact with said molten metal;

(b) means for cooling said first surface portion and solidifying the molten metal in contact with said 10. The structure of claim7 wherein: 10 first surface portion to form a portion of the skin (a) said mold is rectangular in cross section; and of said cast strand;

(b) said first area has a greater lateral dimension at r (c) a second surface portion of said mold in contact one end thereof in contact with molten metal than with said molten metal and disposed in abutting at the other end thereof. lateral relation to said first surface portion, said 11. The structure of claim 7 wherein: second surface portion being so constructed that said (a) said first means is a ceramic material that has molten metal in contact therewith remains molten rnore surface area at one end thereof in contact with and tapered so that the second surface has a greater molten metal than at the other end thereof. lateral dimension adjacent the inlet end than adja- 12. The structure of claim 7 wherein: 90 cent the other end of said mold;

(a) said first means includes a member overlying in (d) a third surface portion of said mold disposed spaced apart relation and joined peripherally to said adjacent both said first and said second surface porfirst area. tions and along the length of said mold; and

13. The structure of claim 12 wherein: (e) means to cool said third surface portion whereby (a) said mold is polygonal in cross section; and 95 molten metal in contact therewith solidifies and (b)said member is peripherally joined to abutting areas of adjacent sides of said mold in said first zone.

14. In the method for producing and withdrawing a cast strand continuously from a mold, the improvement formed solid metal skin;

(e) gradually increasing the perimetrical length of said skin at respective locations of said first area as said partially formed skin advances; and

(f) solidifying the molten metal contacting a third wall area abutting said first and second wall areas forms an additional portion of the skin of said cast strand.

References Cited UNITED STATES PATENTS 30 1 828 335 10/1931 Millspau h 164-122 X comprislng the steps. y a

(a) pouring molten metal into aid Gardner et a1. X (b) solidifying the molten metal contacting a first 33061809 9/ 1965 Hefrmann 164-125 X area of the wall of said mold and forming a portion 313431594 9/ 1967 Dam 164231 of 1a solid lmeltlall skin partially surrounding said 35 FOREIGN PATENTS m0 ten meta w 1e, (c) maintaining in a liquid state the molten metal g contacting a second inset wall area laterally abuterma ting said first area; 927,172 5/ 1963 Great Britain. advancing mm the Pamany 4.0 I. SPENCER OV-ERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner US. Cl. X.R. 

